Commit 921a7acd authored Jan 16, 2018 by Changbin Du Committed by Steven Rostedt (VMware) Jan 23, 2018

tracing: Detect the string nul character when parsing user input string

User space can pass in a C nul character '\0' along with its input. The
function trace_get_user() will try to process it as a normal character,
and that will fail to parse.

open("/sys/kernel/debug/tracing//set_ftrace_pid", O_WRONLY|O_TRUNC) = 3
write(3, " \0", 2)                      = -1 EINVAL (Invalid argument)

while parse can handle spaces, so below works.

$ echo "" > set_ftrace_pid
$ echo " " > set_ftrace_pid
$ echo -n " " > set_ftrace_pid

Have the parser stop on '\0' and cease any further parsing. Only process
the characters up to the nul '\0' character and do not process it.

Link: http://lkml.kernel.org/r/1516093350-12045-2-git-send-email-changbin.du@intel.com



Acked-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Changbin Du <changbin.du@intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

parent 2ee5b92a

kernel/trace/trace.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -1237,7 +1237,7 @@ int trace_get_user(struct trace_parser parser, const char __user ubuf,
		}

		/* only spaces were written */
		if (isspace(ch)) {
		if (isspace(ch) \|\| !ch) {
		*ppos += read;
		ret = read;
		goto out;
		@@ -1247,7 +1247,7 @@ int trace_get_user(struct trace_parser parser, const char __user ubuf,
		}

		/* read the non-space input */
		while (cnt && !isspace(ch)) {
		while (cnt && !isspace(ch) && ch) {
		if (parser->idx < parser->size - 1)
		parser->buffer[parser->idx++] = ch;
		else {
		@@ -1262,7 +1262,7 @@ int trace_get_user(struct trace_parser parser, const char __user ubuf,
		}

		/* We either got finished input or we have to wait for another call. */
		if (isspace(ch)) {
		if (isspace(ch) \|\| !ch) {
		parser->buffer[parser->idx] = 0;
		parser->cont = false;
		} else if (parser->idx < parser->size - 1) {